Electrical connection systems comprising plugs and sockets are often used to connect printed circuit boards which carry electrical components to multiple conductor cables such as ribbon cables. The plug part of the connection system is mounted directly on the circuit board, and the socket part of the connection system is attached to the cable and electrically connected to the conductors of the cable. When the socket is fit into the plug, electrical connection is made between the circuit board and the equipment connected to the cable.
In high density printed circuit board modules, the connection system often takes the form of a ribbon cable terminated in a miniature connector having an array of connector pins, often disposed in two rows. A large number of signals which can be analog or digital, power supply connections, TTL compatible signals, C-MOS compatible signals, and others can be carried through the connector. Clearly, the connector system must be such that the socket fits into the plug in only one way in order to properly make the connections. If the connector is offset or misrotated with respect to the plug, improper connections can be made, with the possibility not only of equipment malfunction, but also of equipment destruction.
To prevent misplugging due to offsetting or misrotation of the socket with respect to the plug, the socket or plug often have interfitting bodies keyed to allow insertion for connection in only one orientation. Thus, the socket can be configured in a particular shape having an outer periphery, and the plug which is positioned on the printed circuit board can have a frame defining an interfitting outer periphery so that the socket fits into the plug in only one orientation. Coding projections/coding grooves or other keying mechanisms can also be used on the plug, the socket, or both of those elements in order to assure that connection is made in only one orientation.
Such connector systems are used in printed circuit boards but can raise difficulties when a high degree of miniaturization is a requirement. The need for the plug to be configured within an encircling frame which surrounds the socket usually imposes a requirement that a reasonably substantial area beyond the actual connector pins be dedicated to the connection system. In other words, the plug which must be mounted on the printed circuit board, when it carries its own peripheral mating frame for the connector, demands a surface area on the printed circuit board which is substantially larger than the area needed solely for the connections. Furthermore, because the plug which is mounted to the circuit board requires this extra space for the peripheral keying elements, the electronic components on the printed circuit board must be displaced adequately from the plug to allow mounting of the plug on the board without interference from the electrical or electronic components. Thus, the plug not only uses the actual space which it occupies, including the space necessary for the peripheral keying elements, but also requires that electrical components mounted near the plug be displaced from the plug itself, requiring a relatively large circuit board surface area; that is a requirement which can be incompatible with extreme miniaturization when it is desired.
An alternative, of course, is to provide a plug without the encircling peripheral keying elements, but that raises the problem of potentially misconnecting the socket and the plug. As noted above, misorientation can result in improper electrical connections, which in turn leads to circuit malfunction or equipment failure.
Attempts have been made to provide an open plug on a printed circuit board, that is, a plug without an encircling peripheral keying frame element, and to provide some means of keying the connector to the plug. For example, when connectors are of the two-row variety, a different number of connector pins can be disposed in each row, such that the socket fits properly on the plug in only a single orientation. Connectors of this sort are a familiar means of connecting peripheral devices to personal computers.
In addition to the connectors which use different numbers of pins in each of two rows, other keying arrangements have been utilized, such as single or multiple row plugs in which a pin is missing from a particular location in the plug, and the socket has a plugged bore at the corresponding location. If the socket is misaligned, it cannot therefore be plugged onto the plug.
In both of these cases, if one attempts to plug the socket onto the plug in a way which is not allowed by the keying system, the possibility exists of bending of the pins or other deformation of the plug or socket which can destroy the socket, the plug, and perhaps the circuit board. The possibility of damaging elements which are keyed by virtue of rather thin connecting pins and the like is appreciated when one contrasts the insertion or removal force of a plug when properly oriented, with the not-substantially greater force required to damage the plug if it is misoriented. Thus, while in theory such connector pin type keying systems should be adequate for their intended purpose, in many applications they are subject to failure as has been described herein.
Other means are available for assuring that plugs in this environment are properly mated, such as electronic systems which sense connections between desired pins to drive plug-sensing circuitry, and generating an enabling signal only when the plug is properly connected. However, such systems require the dedication of pins in the plug to the connection assurance function, and are not adapted to actually prevent misconnection, but only to signal a misconnection when it is made.